Had it not been for Johnston, the vaccine trial leading to this critical finding may not have happened. Johnston serves as the director of the Vaccine Research Program within the National Institute of Allergy and Infectious Diseases' (NIAID) Division of AIDS.

The vaccine trial was publicly opposed by 21 respected scientists as a 'waste of the government's money.' Johnston and three colleagues published a rebuttal in the same leading scientific journal, and the NIAID — through Johnston's program — funded 75 percent of the project.

"It's going to take a while to build on this promising result," Johnston allowed. "I'm hoping that within my lifetime there will be an AIDS vaccine ready for broad distribution."

Prior to her current position, which she's held for 13 years, Johnston was an instrumental figure in the NIH's drug discovery area.

"I was involved in overseeing, in retrospect, some very important areas of research that laid the foundation for showing that drugs can prevent mother to child transmission of HIV," she recalled.

After nine years there, however, she believed she could make a bigger difference and left NIAID to serve as the founding scientific director of the International AIDS Vaccine Initiative before returning to NIAID in her current role.

"I'd been involved in a lot of advances in treating infected people, but there weren't substantial advances in preventing new infections," she explained. "I'd done what I could for therapeutics. What we really need is a vaccine — a proven way to stop the spread of infectious disease."

Given the stakes, Johnston is, at times, embroiled in controversy.

"I've taken my punches along the way, but we always try to do what we think is best for the science," she said. "It's knowing that I am part of a team that is tackling one of the most challenging public health problems that ever existed. I'd rather fail at something really big, than succeed at something nobody cares about."

Johnston acknowledges those around her who have made significant contributions to the field, such as fellow alum Stephen Lagakos, who recently passed away.

"We have lost a giant in the field," she said. Lagakos is credited with organizing one of the first AIDS centers in the nation and designing many of the initial nationwide clinical trials to find therapies to treat AIDS.

Johnston views her Carnegie Mellon experience as instrumental.

"The direction my career took is nothing that I ever envisioned when I was studying chemistry at Carnegie Mellon, but it gave me the foundation on which to build. I'm thankful for that," she said. "I also appreciated the diversity of the campus in terms of people and their experiences and their interests. That enabled me to have a career in which I embrace diversity."

Reflecting on her time here, she added, "It's one of the best decisions I've ever made."